1.0. Field of the Invention
The present invention is generally directed to a process for repulping wet-strength paper in which a peroxide compound alone or in combination with a select group of metal salts or chelates oxidizes polymeric resins in the wet-strength paper.
2.0. Discussion of Related Art
Wet-strength paper contains a resin which is adsorbed onto paper fibers during the paper making process and cross-links on heating or aging of the paper to form a polymeric network which adds strength to the paper. Wet-strength resins fall into two groups, permanent and temporary and include formaldehyde-based resins, amine-epichlorohydrin based resins and aldehyde polymers.
In order to repulp wet-strength paper, it is necessary to hydrolyze the cured resin. For many years metal hypochlorites (e.g. sodium and potassium hypochlorite) have been used as reagents for repulping wet-strength paper as shown by, for example, C. S. Maxwell, U.S. Pat. No. 3,407,113 and H. R. Miller, U.S. Pat. No. 3,427,217.
Hypochlorites generate adsorbable organic halides in paper mill effluents. These substances are environmentally undesirable. Accordingly, the papermaking industry has sought to use non-chlorinated reagents for repulping wet-strength paper.
Alkali metal persulfates (M.sub.2 S.sub.2 O.sub.8) and monopersulfates (MHSO.sub.5) have recently been used as reagents to replace hypochlorites. H. H. Espy et al "Persulfates as Repulping Reagents for Neutral/Alkaline Wet-strength Broke" Tappi Journal Vol. 76, No. 2, pp. 139-141 (February, 1993) show significant reductions in organic chlorides using persulfates as the oxidizing agent.
However, there is a continuing need to develop repulping reagents that are environmentally acceptable and which are effective in repulping wet-strength paper during the repulping operation.
3.0. Summary of the Invention
The present invention is generally directed to a process for repulping wet-strength paper in which a non-chlorinated reagent is used to oxidize the wet-strength resin in the wet-strength paper.
In particular, the present invention is directed to a process for repulping wet-strength paper comprising adding at least one peroxide compound alone or in combination with a non-alkali, non-alkaline earth metal salt or metal chelate to thereby oxidize the wet-strength resin in the wet-strength paper to form paper fibers.